Renewable energy, like wind energy and solar energy, is increasingly being explored to meet the ever-growing demand for energy in an environmentally-responsible manner. A photovoltaic (PV) system is an example of a renewable energy system that converts the sun's radiation into usable electricity. PV systems range from small, rooftop-mounted or building-integrated systems with capacities from a few to several tens of kilowatts, to large, utility-scale power stations of hundreds of megawatts. Some PV systems may be connected to an electrical grid to enable transmission and distribution of their generated-electricity to other participants in the utility market. On the other hand, some PV systems, such as, for example, residential or small-scale PV systems, may be off-grid or stand-alone systems.
FIG. 1 is a simplified block diagram of an exemplary renewable energy system 10 with on-site energy storage. In the present disclosure, a PV solar system is used as an example of a renewable energy system. Therefore, the discussion herein is primarily provided in the context of a PV solar system. However, it is understood that the discussion remains equally applicable to other renewable energy systems as well. When the renewable energy system 10 is a typical PV solar system or PV solar site, it may include a renewable Direct Current (DC) energy source 12 in the form of a solar/PV array. The PV system 10 also may comprise a number of Balance of System (BOS) components, three of which—a charge controller 14, a storage (battery) unit 15, and an inverter 16—are shown in FIG. 1 by way of an example. The BOS components 14-16 may balance the power-generating sub-system of the solar array 12 with the power-using side (the electrical load). For ease of illustration, only the Alternating Current (AC) electrical service interconnect point is shown using block 18 in FIG. 1; any DC load portion is omitted. An AC load (such as, for example, a residential electrical load) or AC power grid (not shown) may receive the AC inverter output through the AC interconnect point 18.
The charge controller 14 may regulate the electrical input received from the PV array 12 so as to satisfy the demand for the Direct Current (DC) load (not shown) and transfer any additional electricity for storage into the battery unit 15. On the other hand, when the generated electricity (by the DC energy source or PV array 12) is not sufficient to satisfy the requirements of the DC load, the charge controller may access the stored electricity from the battery unit 15 and supply it to the DC load. The battery or storage unit 15 also may supply electrical energy to an inverter 16, which may convert the stored electric current from DC to AC to be delivered to the AC service interconnect point 18. The DC load (not shown) may represent systems or devices that operate on DC current, whereas the AC interconnect point 18 may serve systems or devices that operate on AC current. Although not shown in FIG. 1, the PV site 10 also may include additional BOS components such as, for example, power-conditioning equipment, structures and racking systems for mounting various BOS components and solar arrays, electrical wiring, cabling, and interconnections, and other electrical accessories to set up a working PV site. In some implementations, the PV site 10 also may use a solar tracking system (not shown) to improve the system's overall performance.